The present invention relates, in general, to electrical watthour meters and, more specifically to watthour meter mounting enclosures.
In the electric utility industry, plug-in, socket-type watthour meters are commonly employed to measure electrical power consumption at a residential or commercial building establishment. A cabinet is typically mounted on an outside wall of the residence or building and contains a meter socket having pairs of line and load contacts which are connected to electric power line conductors extending from the utility power network and electric load conductors connected to the residential or building establishment power distribution network. The contacts receive blade terminals on a plug-in watthour meter to complete an electric circuit through the meter between the line and load terminals mounted in the cabinet for the measurement of electrical power consumption.
S-type, socket-type, plug-in watthour meters have replaced older A base bottom connected meters which were formed of a single piece housing in which the watthour meter was fixedly mounted along with compression terminals which provide connection to the utility power lines and the building load distribution network.
In a installation involving an A-type bottom connected meter, an A to S socket adapter is used to allow a new S-type watthour meter to be installed. The socket type meter has outwardly extending blade terminals which are insertable into the jaw contacts in the cabinet of a S-type meter socket. The socket adapter includes its own set of female jaw contacts which receive the male blade terminals of the S-type plug-in, socket-type meter.
A socket extender adapter used to convert a ringless style socket to a ring-type socket has a similar arrangement of contacts and terminals to plug-in to a socket and to receive an S-type, plug-in, socket-type meter.
While it is typical for a watthour meter, once it is installed in a socket or socket and socket adapter, to remain in service for many years, it is still necessary for such meters to be removed for repair or replacement from time to time as well as to temporarily disconnect electrical service to a particular customer. During the installation and removal of the watthour meter from the socket or socket adapter, the electric power line terminals in the socket or socket adapter remain connected to the electric utility power line conductors and carry potential. The utility employee installing or removing the watthour meter may inadvertently touch such contacts thereby raising the possibility of injury. Furthermore, an inadvertent short across the contacts caused by a tool contacting the contacts or a full fault caused by a 90.degree. offset insertion of the meter can cause a spark or flash which could damage the watthour meter installation as well as posing a significant risk of injury to the utility employee. Various flash covers or shields have been devised as separate attachments to cover a portion of the jaw contacts in a watthour meter socket or socket adapter. One type of flash cover or shield is shown in FIG. 16 and comprises a clip formed of an electrically insulating material which snaps over the outer end of a jaw contact to cover the outermost portions of the jaw contact. The clip includes a central slot or aperture which is aligned with the slot between the two spring legs of the jaw contact to allow insertion of a watthour meter terminal into the jaw contact while the clip is still attached to the jaw contact.
A more elaborate flash cover or shield is shown in FIG. 17. This type of flash shield is formed with a flat front cover containing slots which are aligned with the jaw contacts and receive the watthour meter terminals therethrough. Rearward facing legs extend from the upper and lower portions of the cover and space the cover from the back wall of the socket or socket adapter.
Both types of flash or safety shields provide some measure of flash protection in that they cover a portion of the jaw contacts thereby minimizing the possibility of inadvertent contact with such contacts by the utility employee or portions of the meter during installation or removal of the meter from the socket or socket adapter. However, such previously devised flash covers or shields do not completely surround all exposed portions of the jaw terminals. Thus, such exposed portions may still be inadvertently touched by a utility employee or, in the event of a fault or a short, a spark or flash could still occur.
Thus, it would be desirable to provide a safety shield for an electrical watthour meter apparatus which completely encloses all portions of the jaw contacts in a watthour meter mounting device, such as a socket, socket adapter, socket extender, etc., to prevent inadvertent contact with such jaw contacts or to prevent a short between such contacts which could lead to a spark or flash. It would also be desirable to provide such a safety shield which can be easily incorporated into the design of a new watthour meter socket, or other meter mounting device, socket adapter, or installed as a separate component in an existing watthour meter socket or socket adapter.
In watthour meter socket adapters, solid or stranded conductors are connected between the jaw contacts and the terminals. While such conductors can be easily formed to the desired shape so as to extend between a jaw contact and a terminal, all polyphase adapter designs have required certain of the conductors to be crossed or overlapped. This feature plus the need to allow clearance for the meter feet have limited the maximum current carrying capacity of such conductors. It would be desirable to provide conductors for watthour meter socket adapters which have increased current carrying capacity while still being easily mounted in the socket adapter.
It would also be desirable to improve the design of the jaw contacts and terminals employed in a watthour meter socket adapter. In previous watthour meter socket adapters, the jaw contacts typically have a folded over design formed of a base wall which is fixedly mounted to the shell of the socket adapter and two spaced side walls extending therefrom. The outer ends of the side walls are folded over inwardly between the side walls and terminate in parallel end flanges which slidably receive a blade terminal of a watthour meter. However, this design presents three different problems. First, the direction of current flow through the jaw contacts is opposed to the direction of current flow from the jaw contacts through the blade terminal of the watthour meter. That is, current flows in one direction through the folded over portion of the jaw contacts and then in an opposite direction outward from the jaw contacts through the blade terminal. This creates opposed magnetic fields which increase resistance and generate heat and could possibly lead to a less than reliable connection of the blade terminals to the jaw contacts. Thus, it would be desirable to provide a jaw contact design which has less resistance than previous jaw contact designs.
Secondly, the relatively large angle between the folded over portion and the side walls of the jaw contacts requires a high level of force to insert a watthour meter blade terminal into a jaw contact. This is due solely to the angle of the folded over portion of the jaw contacts which generates a sideways force to separate the jaws as well as an axial force to insert the blade terminal through the parallel end portions of the jaw contacts. Thus, it would be desirable to provide an improved jaw contact design for a watthour meter socket adapter which provides reduced insertion force to mount a watthour meter in the socket adapter.
Thirdly, the removal of the blade terminals of a watthour meter from the folded over jaw contacts commonly employed in previous socket adapters also requires a high level of force. Such a high force is difficult to apply to the watthour meter due to the round glass dome on the meter. The high removable force results from the tendency of the folded over portions of the jaw contacts to tighten since the inner folded over ends of the jaws pulls upward during removal of a blade terminals from a jaw contact. Thus, it would be desirable to provide a jaw contact design for a watthour meter socket adapter which requires reduced watthour meter withdrawal forces.
Finally, in previously devised conductors for socket adapters, the jaw contacts have been attached to the conductors by threaded fasteners. This involves labor intensive and costly manufacturing operations in order to prepare the threaded apertures in the conductors and the contacts and to insert and tighten the fasteners. Thus, it would be desirable to provide a conductor and jaw contact design for a watthour meter socket adapter which requires less labor for manufacturing and assembly and thereby has a reduced cost and greater reliability.